Genetic consequences of Last Glacial-Holocene changes in snowfall regime in Arnica mallotopus populations: A plant confined to heavy-snow areas of Japan.

PREMISE: Snow is an important environmental factor affecting plant distribution. Past changes in snowfall regimes may have controlled the demographies of snow-dependent plants. However, our knowledge of changes in the distribution and demographies of such plants is limited because of the lack of fossil records. METHODS: Population genetic and landscape genetic analyses were used to investigate the response of population dynamics of Arnica mallotopus (Asteraceae)-a plant confined to heavy-snow areas of Japan-to changes in snowfall regimes from the Last Glacial Period to the Holocene. RESULTS: The population genetic analysis suggested that the four geographic lineages diverged during the Last Glacial Period. The interaction between reduced snowfall and lower temperatures during this period likely triggered population isolation in separate refugia. Subpopulation differentiation in the northern group was lower than in the southern group. Our ecological niche model predicted that the current distribution was patchy in the southern region; that is, the populations were isolated by topologically flat and climatically unsuitable lowlands. The landscape genetic analysis suggested that areas with little snowfall acted as barriers to the Holocene expansion of species distribution and continued limiting gene flow between local populations. CONCLUSIONS: These findings indicate that postglacial population responses vary among regions and are controlled by environmental and geographic factors. Thus, changes in snowfall regime played a major role in shaping the distribution and genetic structure of the snow-dependent plant.

Identification of management units in threatened populations of Arnica mallotopus Makino (Asteraceae) using novel EST-SSR markers.

Arnica mallotopus is a perennial herb endemic to the snowy regions of Japan. At the southern edge of its distribution, in Kyoto Prefecture, overgrazing by sika deer and decreased snowfall have resulted in the rapid decline of A. mallotopus populations. Therefore, there is an urgent need for a conservation genetic analysis of the remaining local populations. In this study, we first developed 13 EST-SSR markers to evaluate genetic variation in A. mallotopus. The average number of alleles per locus was 5.33. Genetic analysis using these markers showed that the investigated samples were classified into two groups corresponding to landscape structure. One group isolated from a tributary of the Yura River showed a strong population bottleneck signal, likely resulting from founder effects and subsequent drifts. On the other hand, the genetic diversity of the second group in the main distribution along the Yura River was higher and less inbred. Overall, our assessment suggested recognizing the two genetic groups as management units in conservation programs for the threatened populations.